The invention relates to a coated web printing paper suitable for printing with cold-set offset printing ink.
If one commonly refers to offset printing, offset printing with heat-set printing inks is typically intended, and not the use of an offset process using cold-set inks. The cold-set process is predominantly used for the printing of newspapers on uncoated newsprint paper, and the printing presses used are therefore commonly referred to as newsprint printing presses.
The heat-set offset process, on the other hand, covers an entirely different field of application, and is, similar to the rotogravure process, predominantly used for high quality multi-color printing applications on coated, high-finish supercalendered papers up to the highest grades.
A patent which is believed to describe such conventional supercalendered papers suitable for heat-set offset printing is U.S. Pat. No. 4,820,554 to Jones et al. An object of the Jones et al. patent is to provide a chemically modified kaolin based pigment that shows enhanced gloss development during supercalendering of a paper coated with a coating formulation which contains this modified pigment. In order to demonstrate the improved gloss development, the patent includes a number of examplesxe2x80x94such as Examples XVI, XVII and XVIIIxe2x80x94in which certain base papers were coated with a coating formulation including various proportions of the modified kaolin, and the properties of the papers then tested. For comparison purposes, a coating formulation containing as pigment 100% Betagloss, a standard kaolin brand from E.C.C. America, was used.
The pigments used and the test papers prepared in the Jones et al. patent appear in all respects to be those typically used for conventional heat-set offset printing, and thus unsuited for the cold-set offset printing method. The example portion of the present application provides a comparison of the properties of the paper according to the claimed invention with that prepared according to the teachings of the Jones, et al. patent, demonstrating the clear differences between the papers according to the claimed invention and those prepared according to the teachings of the Jones et al. patent concerning suitability for the cold-set offset printing process.
It is understood by those skilled in the art that uncoated, common newsprint paper has a high receptivity for liquids, due to the absence of a paper coating. This is why it has been possible to use a printing ink which is absorbed quickly and therefore dries quickly, so that no additional energy in the form of heat or other radiation energy is necessary to assist printing ink drying. The newsprint printing presses are therefore designed accordingly.
Because newsprint presses remain idle for much of the day, there was a desire to use these presses for higher-quality printing applications during this idle time. Yet, conventional magazine grade coated papers designed for heat-set and rotagravure printing processes proved unsuitable for use on newsprint presses. There was therefore a need to provide a commercially successful machine-coated paper which could be processed on newsprint presses in the speed range applied for the printing of uncoated newsprint.
A matte paper having generally suitable characteristics for cold-set offset printing is described in EP-A 0 785 307. As regards the need for enhanced cold-set paper qualities and the related problems, the introductory statements in this older document are helpful.
However, the web printing paper described in EP-A 0 785 307 is only of a so-called matte quality. It is explained in this document that to achieve the pressability and printability of a coated web printing paper in the cold-set offset process, special demands must be made on the paper regarding its wetting/water penetration behavior and its ink absorption speed. These are properties which at times are in turn considerably disadvantaged by a glazing on smoothness of from 1,000 to 1,600 sec. Bekk, as is necessary for producing typical smooth papers. For this reason, it was only possible according to this document to provide a coated matte quality paper suitable for the cold-set offset process. High smoothness and gloss, which indicate surface compaction, are thus generally detrimental to cold-set applications.
A high degree of advertizing effectiveness is presently desired through the use of newspaper supplements, and only glossy paper can be considered for certain advertizing orders. In the absence of cold-set-suitable glossy low weight coated (LWC) papers, these brochures are still printed via the conventional heat-set process as before. To enable the cold-set printer to take on such printing orders as well, the main point leading to the present invention was a desire to develop a glossy paper quality that closes this quality gap, and which can be pressed and printed without problems via the printing machine configurations that are typical in the newspaper printing domain (eight-tower and satellite printing machines). After such a paper quality has been established in the domain of mass-produced printing paper, economic aspects were also to be taken into consideration.
It was therefore an object of the claimed invention to provide a coated web printing paper for the cold-set process that has sufficient gloss for more demanding printing products, in particular advertizing supplements and the like, and which can be manufactured economically.
This technical problem is solved by the features of the claimed invention.